The present invention relates to a lead frame for wire-bonding and a method of forming a semiconductor device by use of the lead frame.
FIG. 1 is a plane view illustrative of a lead frame to be used for wire-bonding and resin-sealing. Lead frames 2 radially extend from an island 4. A tie-bar 7 extends across the lead frames 2 so that the tie-bar 7 is in the form of the four sides of square. A gate 8 is formed at one corner of the square. The bonding processes will be described with reference to FIGS. 2A through 2D.
With reference to FIG. 2A, a wire 1 is bonded by a capillary 5 on a pellet 3 on an island 4 around which leads 2 are provided.
With reference to FIG. 2B, the capillary 5 is moved toward the lead 2 to form a loop of the wire 1 which extends between the pellet 3 and the lead 2.
With reference to FIG. 2C, the capillary 5 is achieved to the lead 2 and the wire 1 is bonded to the lead 2 by the capillary 5 so that the wire 1 is bonded between the pellet 3 and the lead 2.
With reference to FIG. 2D, the capillary 5 is released from the lead 2.
The conventional resin sealing process will subsequently be described.
With reference to FIG. 3A, the wire-bonded pellet and the leads are placed in cavity of dies 9.
With reference to FIG. 3B, a molten resin 10 is flowing from the gate positioned at a corner to fill up the cavity of the dies 9 in which the wire-bonded pellet and the leads are placed.
With reference to FIG. 3C, the molten resin 10 has filled up the cavity of the dies 9 and the wire-bonded pellet and the leads are sealed with the resin 10.
FIG. 4 is a plane view illustrative of wires extending between the leads and the pellet on the island after the sealing resin has filled up the cavity of the dies and has sealed the semiconductor device. The molten resin was flowing from the gate 8 into the cavity of the dies 9. Each wire is fixed at opposite ends to the pellet and the leads but not fixed at intermediate portions thereof. The wires extending in a direction nearly parallel to the flow direction of the molten resin are not so carried. By contrast, the wires extending in a direction nearly vertical to the flow direction of the molten resin are largely carried by the flow of the molten resin.
Particularly when the density of the wires is high, it is possible that the wires are largely carried by the flow of the molten resin so that the wires are made into contact with each other thereby to form a short circuit. At the corners, the distance of the adjacent two wires is narrower than the other positions, for which reason the wires at the corners are likely to be made into contact with each other thereby to form a short circuit.
In the above circumstances, it had been required to develop a novel lead frame structure which prevents the each wire from being largely carried by the flow of the molten resin thereby to prevent formation of short circuit.